1. Field of the Invention
The present invention relates to ice making machines, more particularly to an improvement of the refrigeration system in the ice making machines.
2. Discussion of the Prior Art
In conventional refrigeration systems, an externally equalized type of thermostatic expansion valve is disposed within the refrigerant inlet line of an evaporator coil taking into account the pressure drop at the evaporator coil. The expansion valve is associated with a thermostat bulb located on a refrigerant return line leading from the evaporator coil back to a refrigerant compressor and an external equalizer is connected to the return line at a position adjacent the thermostat bulb. Under control of the thermostat bulb and external equalizer, the expansion valve acts to control the amount of refrigerant supplied therefrom into the evaporator coil in accordance with the temperature detected by the thermostat bulb and the pressure detected by the external equalizer. During the defrost cycle of the ice making machine, the difference in pressure between the inlet and outlet sides of the evaporator coil increases due to the flow of hot gases directly supplied into the evaporator coil from the compressor through a solenoid valve for hot gas in a bypass line of the refrigeration system. As a result, the expansion valve may not be fully closed during the defrost cycle. For this reason, the temperature of refrigerant supplied into the evaporator coil does not rise to a desired value, resulting in deterioration of the defrost efficiency. If a maximum working pressure acting on the expansion valve was lowered to fully close the expansion valve during the defrost cycle, the freezing efficiency of the ice making machine would be deteriorated.